The light guide of automobile lamp is generally about 8 mm in diameter, with a plastic solid circular tube of a certain length, and there are light guides in other cross-section shapes, for example, square. An end part of light guide is provided with light source, and the light rays emitted by the light source transmits within the light guide through total reflection after penetrating into the internal part of light guide. For the distance of the light source from the end face of light guide and the position thereof directly affect the amount of light rays emitted by the light source into the internal part of the light guide, it is required to precisely control the distance of the light source from the end face of the light guide so as to ensure a stable light-emitting effect of the light guide.
A traditional mounting method for the light transmission device for automobile lamp is to respectively fix the light guide and assemblies comprising the light source to a fixing bracket, and generally there is a connection between several fixing brackets. Due to the precision of assemblies themselves and the accumulative errors as caused by multiple assembling, it is hard to well control the distance of the end face of light guide from the light source and the position thereof.
At present, a frequently-used mounting method of light guide is as shown in FIG. 1, the light guide is inserted into the fixing bracket and reaches the contact surface, being fixed through the elastic backoff. Namely, when the light guide is inserted, the elastic backoff deforms and expands, and when the light guide is inserted and reaches the contact face, the elastic backoff resumes to natural state, forming fixation for the light guide.
Defects of this mounting method are:
(1) Due to the elasticity of the light guide, it is hard to press it in place when assembling.
(2) Generally two or three elastic backoffs are installed to realize the stability of fixation, which makes it hard to judge whether all snap joints have been installed in place, namely, it is hard to judge whether other snap joints have locked the light guide after a certain snap makes it.
(3) For the convenience of assembling, generally, a little gap is left between the snap joint and the lug boss of light guide, which causes improper positioning of the light guide, to be precise, there is a little movement after the light guide is mounted in place, which causes a range of deviation of the distance of light guide from LED light source.